Very strange audio interference DR-40

[nunoaymar]

Hi, I'm new to this forum, but I really need your help please!

I just bought a used DR-40 recorder and tested it, the internal microphone worked perfectly, but when I tested a dynamic microphone on the external output, there was a very strange noise that seems to respond to the electrical impulses on the screen. As he records, a noise is heard every second, perfectly synchronized with the recording count on the screen, and it's all the time! I'm using the battery-powered recorder in MIC mode.

I'm new to this type of equipment, but I took great care in sound testing. I would like to know at least what's going on ...

 

[Geoffrey Kolbe]

How does this noise vary if you increase or decrease the recording volume?
Is the noise only there when the microphone is plugged in?

 

[BazzBass]

try the Mic in a pa or amp to test it's not faulty
swap the cable to test it's not the cause
what's going in to the DR, XLR , TS or TRS connector?